Global Illumination

Global illumination is a superset of radiosity and ray tracing.
The goal is to compute all possible light interactions in a given
scene, and thus obtain a truely photorealistic image. All combinations
of diffuse and specular reflections and transmissions must be accounted
for. Effects such as colour bleeding and caustics must be included
in a global illumination simulation.

Most of the images here have been rendered using
photon mapping. Others have been
rendered using techniques described in the papers on my
papers web-page.

The Courtyard House with Curved Elements

This image from the animation "The Light of Mies van der Rohe" demonstrates
how photon mapping can be used compute global illumination in a complex
model. The sun is the only light source and most of the light in the
image is due to indirect illumination. The animation can be found on
the animations web-page.

Teapot illuminated by a high dynamic range environment

Metal teapot

Diffuse teapot

Glass teapot

Glossy teapot

The classic teapot illuminated by a high dynamic range environment (grace
cathedral lightprobe by Paul Debevec). Environments such as this provide
an easy way to achieve realistic lighting. With complex environment maps
it pays to use structured importance
sampling - except for specular materials.

Cornell box replica - rendered using photon mapping

This is a replica of (one of) the cornell box model first used
at the graphics lab. at Cornell. It is a typical radiosity scene
with polygonal faces and diffuse materials. Here it is rendered
using photon mapping.

This is a daylight simulation of Little Matterhorn.
Just 100,000 photons were used to simulate indirect illumination
of the landscape. For the cloudy day, I used a simple
procedural technique to create a layer of true volumetric clouds
that would cover the landscape and still provide sufficient detail.
Note the shadows on the landscape from the clouds and how the tip
of Little Matterhorn sticks into a cloud. The model of
Little Matterhorn was created at University of Utah. There
is an animation of the clouds forming over the landscape on
the animations web-page.

This simple box model has mostly indirect illumination and many
global illumination algorithms have trouble rendering the
indirect illumination (through the glass windows) accurately.
Photon mapping works quite well in this case where the
initial sampling of photons from the lights provides a
very powerful estimate for the rendering phase. The model
was made by Christophe Valtin.

A diffuse Jaguar model rendered with pathtracing

This is a simple diffuse model of a Jaguar with 140000 triangles,
and a big diffuse skydome. It was rendered with pathtracing
in 1024x512 in 20 min. on a PIII-500. This is one of the few
cases were path tracing is resonable fast. However, eliminating the
last noise would probably require several orders of magnitude
more computation. Today, this type of rendering with a big white
skydome light source has been popularized under the name of ambient
occlusion.

Ray Tracing, Photon Mapping, and Global Illumination

Ray tracing1.5 seconds

+ soft shadows7 seconds

+ caustics12 seconds

+ global illumination15 seconds

Path tracing reference

Cornell box series showing the effect of simulating global illumination.
All the images have been rendered at 1024x768 with 4 samples per pixel
on a Dual P3 800MHz Linux-PC. The ray tracing version took 1.5 seconds,
The version with soft shadows took 7 seconds. Adding caustics increased
the rendering time to 10 seconds and 2 seconds of photon tracing.
The global illumination version took 12 seconds to render and 3 seconds
of photon tracing time. For this scene the global photon map has
200,000 photons and the caustics photon map has 50,000 photons.

Finally, the path tracing reference image on the right
took a long time to render. The important thing to notice is that it
looks the same as the version rendered using photon mapping.

A Museum

The museum image was rendered using the photon map based two-pass global
illumination method. It took 45 minutes to render on a 100Mhz Pentium.
This was one of my early images using the full two-pass algorithm. Note
the anisotropic shading of the cylinders as well as the caustic on the
non-diffuse teapot from the anisotropic cylinder.

A Metalring

Try illuminating a metalring on a table and you will see a nice cardioid
caustic on the table. This shape is easy to describe mathematically and
it is often used to illustrate caustics created as light
from the light sources is reflected or transmitted via specular
surfaces. See the caustics images for
more examples on caustics.

A Desk

This is a path tracing rendering of a simple desk scene. The image was
rendered using 2000 samples per pixel, and in order to render it in
finite time I ran a parallelized version of my renderer on 30 SGI workstations
(MIPS R3000) - still the rendering time was roughly 30 hours!
Notice that no importance sampling was used here as described in the
Rendering Workshop 95 paper
- this is the reference image.